Electrical measuring apparatus



E. F. NORTHRUP.- ELECTRIC-AL NIEASURING APPARATUS. APPLICATION r1LEDJuLY15.191s.

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fa Ano/swf? Patented Apr. 19, 1921.

.TEDWIE NORTHRUP, OF PRINCETON, NEW JERSEY, ASSIGNOB T0 PYROLECTRIC INSTRUMENT CO., 0F TRENTON, NEW JERSEY, A'CGRPORATIN OF NEW JER- SEY.

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Application le'tl July 15,

To all cvwmjt may concern.'

Beit known that I, EDWIN F. NORTHBUP, a citizen of the United States, residing at Princeton, county of Mercer, State O New Jersey, have invented new and useful Electrical Measuring Apparatus, of which the following is a specification.

My invention relates' to electrical measuring apparatus, and more particularly to an electrical pyrometer. j

. My invention resides in electrical measuring apparatus comprising a galvanometer, such as a milliammeter, galvanometer or similar instrument, preferably comprisinga coil movable in a permanent magnet field, the galvanometer being first associated with .a source of electro-motive-force of unknown value, such as a thermo-couple, in such circuit arrangement'that by zero deflection of the galvanometer an electro-motiVe-force equal and opposite to the electromotive force or" the unknown source or thermocouple is determined, the galvanometer later being placed in a circuit arrangement such that by its deflection it indicates the value or" y the unknown electro-motive-torce'or teinperature of the thermo-couple, switching mechanism being lprovided for then connecting the thermo-couple or other source ot unknown electro-motive-force in an isolated circuit with the galvanometer and an adjustable resistance or rheostat which is adjusted to suclnresistance value that the galvanometer will again deflect to the same extent under influence only of the thermocouple or source of electro-motive-force; the apparatus may then 'be used as a direct reading system for measuring temperatures or electro-motive-forccs of a'thermo-couple or other source of current, the apparatus used in the preliminary steps being in eect apparatus for adjusting or calibrating the circuit ot' the thermo-couple and galvanometer to proper resistance value.

Or otherwise stated, my invention comprises apparatus of the character disclosed in my prior Patents Numbered 1,245,609 and 1,245,956, November 6, 1917, with which is included an adjustable resistance or rheostat and suitable switching mechanism for isolating the galvanometer and thermo-couple in a circuit with the rheostat or adjustable resistance, the latter bringing'the resistance ot the entire circuit to proper value to insure Specification of Letters Patent.

ELECTRICAL MEASUBZING APPARATUS.

ratentea apr. ia, aaai.

191s. serial No. 244,919.

electroLmotive-force. `When the switch a is closed, current-from the battery E passes through the resistances T and r1. ln a circuit or 'branch in parallel or shunt with a variable portion of the resistance in circuit with thebattery E, as a variable portion of the resistance r, are the serially connected resistances b, h1, g and it, one terminal of the resistance it being connected by conductor z' with one terminal of theresistance r. The

amount of resistance b in the shunt or i parallel branch or circuit is variable simultaneously with Variation of the resistance 7' by the double contact device y which simultaneously passes over both resistances r and One terminal of the resistance b1 connects by conductor c with the contact spring al carrying the contact Z1 normally in engagementwith the contact spring e connected by conductor to one terminal of the resistance g. A second contact spring d2, adapted to be engaged by the contact (Z1, is

connected with a similar contact spring d3 adapted to be engaged by the contact s1 on the contact spring s connected by conductora with one terminal of the galvanometer A. The contact s1 is normallyl in engagement with thecontact spring Q connected with one ot the binding posts o to which is connected the lead n from the thermo-junction T or other source of electro-motive-force. whose other terminal connects through lead j with thek binding post 7c, which connects byy conductor m with one terminal of the adjustable resistance or rheostat R and with one terminal of each of the resistances r and h.

The galvanometer A, such as a milliammeter, is preferably of the well known DArsonval type of direct current measuring instrument comprising a coil movable in a permanent magnet lie d. It has a scale or scales o with which cooperates the needle or pointer w actuated by the' moving coil of the'instrument. The scale o may be calibrated in any desirable or suitable units and j the scale may'be calibratedv in units of voltage, as millivolts, or in units of temperature, or both. The remaining terminal of thegalvanometer A connects te a point between the resistances g and h through the conductors p and p1 connected, respectively, to the contact springs p2 and p4, p2 carrying a contact p3 normally in engagement with the spring contact p4. vlThe contact p is adapted to engage also the contact spring p5 connected to the movable contact or rider c1 of the adjustable resistance or rheostat R.

In circuit with the battery E and the resistances r and r1 is the normally closedswitchzcomprising the contact spring p6 carrying the contact p7 normally in engagement with the c'ontactspring p8, the springs p6 and p8 being connected, respectively, by conductors c2 and 03 to the switch a and resistance 1'. i

By pushing downwardly upon the button b2 the conical or tapering member 53 thrusts the lower ends of the contact springs d and s apart, causing the contacts d1 and s1 to leave the contact springs e and g and to engage the contact springs d2 and d3. Similarly, pushing downwardly upon the button b4 causes the member b5 to push the contact springs p2 and p6 apart., causing contact p3 to separate from contact spring p* and to engage *contact spring p5, and to cause contact p7 to separate from contact spring p8.

The operation is as follows:

With the contacts d1, s1, p3 and p7 in their normal positions indicated in the drawing, the contact y is moved to such position upon the resistances c and b that the galvanometer A does not deflect or indicates Zero current therethrough. This means that the Source of current of' unknown electro-motive-force, as thermo-couple T, which is in series in this position of the switching mechanism with the galvanometer A and in a path in shunt to the resistance z,'has 0pposed to it an equal and opposite electro- Inotive-f'orce which is the fall of potential across the resistance 71, caused by current from the battery. E. The button b2 is now depressed, separating contact d1 from contact spring e and bringing it into engagement with contact spring d2, and simultaneously separating contact s1 from contact spring g and bringing it into engagement with the Contact spring cl3. This switching operation cuts out of circuit the thermocouple T and the resistance g, and has brought the galvanoineter A into series relation with the resistance h in place of the resistance g, whose magnitude and temperature coefficient are preferably equal to the resistance and temperature coefficient of the galvanometer A including its moving coil or any associated resistance, as described in the aforesaid Letters Patent No. 1,245,956. The galvanometer A will now be traversed by a current of the same magnitude that was previously flowing through resistances g and 71 and the resultant deflection indicates either the temperature of the thermocouple T, or its electro-motive-force, vor both if the instrument is provided Witlnboth a potential and a temperature scale.

The' deflection or reading of the galvanometer A having thus been taken for the then temperature of the thermo-couple T, the pressure upon button 52 is released, and the member b3 returns to normal position indicated under the influence of the spring, not shown. The button b4 is then depressed, and may beheld in thedepressed position gy any suitable stop or lock, not shown.

his causes contact p3 to engage the contact spring p5 and` contact p7 to separate from contact spring p8, the latter operation opening the circuit of the battery E.v We then have the galvanometer A connected in a closed circuit through the switch s, g in series with the thermo-couple T, conductor m, adjustable resistance or rheostat R, and through the now closed switch p2, p5. When this circuit arrangement has been established, the rider c1 is adjusted along the resistance r to' that position which will bring the needle or pointer fw of the galvanometer A back to the same position of deflection occurring upon depression of the button b2 as above described. This means that there is now flowing through the galvanometer A a current of the same magnitude as before, and, the temperature of the thermo-couple being the same as before, because the switching operations are so quickly accomplished, the resistance of the thermo-couple circuit through its leads, galvanometer A and resistance R, is now the proper resistance to insure that the thermo-couple T, even when at new or different temperatures, will as a source of current cause passage of the correct amount ofcnrrent through the galvanometer A to cause a deflection which will directly indicate either the electro-motiveforce of the thermo-couple or its temperature, the temperature scale of the instrumentl A of course having been predetermined for Athe particular thermo-couple used.

In 'this way the readings of temperature or electro-motive-fol'ce may be taken with the thermo-couple connected simplyA in. series with the galvanonleter A, and the amount of' resistance in the circuit may be checked from time to time by reverting to the adjustment of the ccaitact g/ and operai ton b2.

tion of the switching mechanism by the but- It the resistance of theV thermocouple circuit when in series with the galvanometer A and resistance R does not vary, checking is not necessary; but inasmuch as lead resistances or other resistance in the circuit may from time to time vary, the above described checking becomes necessary, and the instrument is checked Whe'never it is believed that a change in the resistance of the thermos-couple circuit may have occurred.

The switch a will ordinarily be opened when the apparatus is out of use. This may be done manually, or it may result automatically from actuation after predetermined movement of the contact device y, as, for example, when the latter is moved off of the resistances 1^, I).

'hile in accoirdance with the patent statutes I have herein illustrated and described the preferred embodiment of. my invention, it will be understood that my invention is notlimited thereby and its scope is to be determined b v the appended claims.

what l claim is:.

l. T he combination with a resistance., ofa deflection instrument and a source of electro-motive-force of unknown value connecti ed in series with each other in a path in parallel to a'- path including said resistance, means for passing through said resistance a current of magnitude causing therein a tall of potential equal to the unknown electro-motive-force of said source, mea-ns for disconnecting said source of electro-motiveforce of unknown value and for connecting said deflection instrument in a circuit relation causing said instrument to produce a deflection indicative of thevalue of the unknown electro-motive force, means for connecting said source of electro-motive-force of unknown value and said deflection instrument in an independent circuit, and means for adjusting the resistance of said independent circuit to a value at which said deflection instrument will indicate the value of the unknown electro-mptive-force of said source.

2. The combination with a resistance, of `a galvanoineter and a thermo-couple connected in a path in parallel with a path including said resistance, said galvanometer comprising a coil movable in a permanent magnet tieldf, means-for passing through said resistance a current oi magnitude causing therein a iall of potential equal to the electro-motive-force of said thermo-couple, means for disconnecting said thermo-couple and for connecting said galvanometer in al circuit relation causing said galvanonieter to produce a dellection indicative of the electro-motive-force of said thermo-couple, means for connecting said thermo-couple and said galvanometer in an independent circuit, and means for adjusting the resistance of said independent circuit to a value causing said galvanometer to produce a detlection varying with the temperature or electro-motiVe-force of said thermo-couple.

3. The combination-With a galvanometer and a source of electro-motive-force of unknown value, of a resistance path, said alvanometer and source of electro-motiveforce connected in a branch in parallel to said resistance path, means for passing through said resistance path a current of magnitude causing a fall of potential equal to the unknown electro-motive-force of said source, means for disconnecting saidsoiurce of electro-motive-force of unknown value and for connecting said galvanometer in a circuit relation wherein it is ltraversed by a current of said magnitude, whereby said galvanometer produces a deflection indicative of the value of the unknown electro-motive-force, means 4for connecting said galvanometer and source of electro-motiveforce in an independent circuit, and means for adjusting the resistance ot' said independent circuit to a value causing said galvanometer to produce a deflection indicative of the value of the unknown electro-motiveb force.

4. The combination with a Inilliammeter and a thermo-couple, of a resistance path, said milliammeter and said thermo-couple connected in a branch in parallel with said resistance path, means for passing through said resistance path a current of magnitude causing a fall of potential equal to the unknown electro-motive-torce of said source, means for disconnecting said thermo-couple and for connecting said milliammeter in a circuit-relation wherein it is traversed by a l current oit' said magnitude, means for connecting said thermo-couple and said milliamnieter in an independent circuit, and an adjustable resistance i'or bringing ythe resistance of said independent circuit to a value which will cause deflections of said milliammeter to indicate the electro-motive-forces or temperatures of said thermo-couple.

5. The combination with a circuit including a source of current and resistance. of a branch lcircuit containing resistance and 'connected in parallel with a part ot' said circuit, `a galvanometer and a source of electro-motive-torce of unknown value connected in a patlrin parallelwith said branch circuit, means for adjusting the strength of current in said branch circuit to a magnitude causing a fall oi potential equal to the unknown electro-motive-force ot' said source. means for disconnecting` said source of electro-motive-force ot unknown value and tor connecting said galvanonieter in a' circuit relation wherein it indicates the value ot the unknown electro-motive-force, an adjustable resistance, and switching iio mechanism'for connecting said adjustable Iresistance A1n. a circuit 'with said galval ing a source of current and resistance, of a j branch circuit containinof resistance and connected in parallel with a part of said circuit, a galvanometer and a source of electro-motive-force of unknown value connected in a path in parallel with said branch circuit, means for adjusting the strength of.

K lcurrent in said branch circuit to a magni- Yaotude causing a fall, of potential equal to the unknown electro-motive-force of said source, means for disconnecting said s ource of electro-motive-force of unknown 'value and for connecting said galvanometer in a circuit relation wherein it indicates the value of the unknown electro-motive-force, an adjustable resistance, and switching mechanism for disconnecting said galvanometer from said branch circuit and for connecting the same in circuit with `said source of electro-motive-force and said adjustable resistance.

7. rI`he combination with a circuit including a source of-current and resistance, of a branch circuit containing resistance and connected in parallel with a part of said circuit, a galvanometer and a thermo-couple connected in series with each other in a path in parallel with said branch circuit, means for ad'usting the strength of' current in said branc circuit to .a magnitude causing a fall of potential equal to the electromotive-forcey of said thermo-couple, means for'disconnecting said thermo-couple and for connecting said galvanometer in a circuit relation whercin it indicates the value of the electro-motive-force of said thermo.- couple, an adjustable resistance, and switching mechanism for connecting said adjustable resistance inl circuit with said galvanometer and said thermo-couple and for interrupting said first named' circuit.

8. The combination with a icircuit including a source of current and resistance, of a branch circuit containing .resistance and connected in parallel with a part of said circuit, a galvanometer and a thermo-couple connected in series with each other in a path in parallel with said branch circuit, means for adjusting the strength of current in said branch circuit to a magnitude causing a fall of potential equal to the electro-motive-force of said thermo-couple, means for disconnecting said thermo-couple and for connecting said galvanometer in a circuit relation wherein it indicates the value of the electro-motive-force of' said thermo-couple, an adjustable resistance., and switching mechanism for disconnecting said galvanometer from said branch circuit and for connecting the same in circuit ywith said thermo-couple andl said adjustable resistanc'e.

9. The combinationA with a deflection instrumenty and a source of electro-motiveforce of unknown value, of means for producing a potential difference equal to lthe electro-motive-orce of said source, switch-A ing mechanism having' one position in which said deflection instrument` is simultaneously subjected to said potential difference and the electro-motive-forceof said source in opposition to each other, said switching mechanism in another position disconnecting said source of electro-motive-force and bringing said deflection instrument into a circuit relation with said means causing said instrument to produce a deflection indicative of the value of the electro-motive-force of said source, means for connecting said source of electro-motive-force and said'deflection instrument in an independent circuit, and

ence and the electro-motive-force of said thermo-couple in opposition to each other, said switching mechanism in another position disconnecting said thermo-couple and bringing said deflection instrument into a circuit relation with said means causing said instrument to produce a deflection indicative 0f the value of the electro-motiveforce of said thermo-couple, means for connectin'g said thermo-couple and said deflection instrument in an independent circuit, and means for adjusting the resistance of said independent circuit to a value at which said deflection instrument will indicate the value of the electro-motive-force of said thermo-couple.

In testimony whereof I have hereunto affixed my signature this 12th day of July, 1918.

EDWIN I?. NORTHRUP. 

